Many of the photoelectric conversion devices used for optical sensors or solar cells use semiconductor crystals such as Si and GaAs, and require precise doping control, control of a pn junction interface or a Schottky interface, and microstructure fabrication techniques.
Further, many of the photoelectric conversion devices used for solar cells are pn-junction-type photoelectric conversion devices formed on Si substrates, and their availability for use is limited to sunlight having wavelengths equal to or shorter than 1.2 μm due to the band gap of Si, and therefore, they are mainly used for performing photoelectric conversion of visible light having wavelengths equal to or shorter than 0.8 μm.
On the other hand, with regard to the photoelectric conversion devices used for optical sensors, a high speed optical sensor in which a Au metal layer with a thickness equal to or greater than several micrometers is laminated on an n-type Si has been known since the 1960's as a sensor for detecting light in the visible range. In addition, various kinds of Schottky type photoelectric conversion devices which respond to light in the infrared range are known, including an optical sensor for detecting light having wavelength bands of from 1 to 2 μm, composed of CoSi2 (polycrystal)/n-Si (Non-Patent Document 4), an optical sensor for detecting light having wavelength bands of from 1 to 5 μm, composed of CoSi2/p-SiGe (Non-Patent Document 2), an optical sensor for detecting light having wavelength bands of from 1 to 6 μm, composed of Pt/p-Si (Non-Patent Document 3), and an optical sensor capable of detecting light having wavelength bands of up to 10 μm, composed of Ir/Si (Non-Patent Document 4).